Heat-recoverable articles such as heat-shrinkable tubes and heat-shrinkable caps that have heat shrinkability in the radial direction are used in covering for, for example, protection, insulation, waterproofness, and corrosion prevention of a connected portion of insulated electric wires, a wiring terminal, a metal tube, or the like. For example, when a connected portion of insulated electric wires is covered with a heat-shrinkable tube and heated, the heat-shrinkable tube shrinks so as to conform to the shape of the connected portion and comes in close contact with the connected portion. Thus, the heat-shrinkable tube can protect the connected portion. In the case where high adhesiveness is required for a connecting portion for the purpose of achieving waterproofness or the like, a multilayered heat-recoverable article that includes an adhesive layer formed on an inner circumferential surface of a cylindrical base material layer is used.
The adhesive layer of such a multilayered heat-recoverable article is formed by using a hot-melt adhesive containing an ethylene-vinyl acetate copolymer (EVA), an ethylene-ethyl acrylate copolymer (EEA), a polyamide, or the like. Such a multilayered heat-recoverable article is produced by respectively forming an outer base material layer and an adhesive layer formed on the inner circumferential surface of the base material layer by extrusion molding so as to have a tubular shape, then increasing the diameter of the resulting tube under heating, and conducting cooling to fix the shape of the tube. After the extrusion molding, the base material layer may be cross-linked by irradiation with ionizing radiation (refer to, Japanese Unexamined Patent Application Publication No. 2000-129042).
Adhesion of such a multilayered heat-recoverable article to an adherend such as an insulated electric wire is performed by, for example, conducting heating in a state where the multilayered heat-recoverable article is arranged so as to cover the outer circumference of the adherend. When the multilayered heat-recoverable article is heated, the base material layer thermally shrinks and the adhesive layer fluidizes at the same time. At this time, the fluidized adhesive layer fills the gap between the adherend and the heat-shrinkable base material layer. Accordingly, by solidifying the adhesive layer by the subsequent cooling, the multilayered heat-recoverable article is brought into close contact with the adherend.